In recent years, various configurations have been adopted to a suspension system of a vehicle such as a four-wheeled automobile. Among these configurations, a bilateral pair of cylindrical trailing arms that extends in a longitudinal direction of a vehicle body and connects the vehicle body with corresponding wheels has been adopted for the rear suspension system of a four-wheeled automobile.
Because the wheels need to be attached to the trailing arms, it is necessary to provide a member for attaching the wheels in the trailing arms. As the member for attaching the wheels in the trailing arms, there is provided an end plate being a plate-like metal member.
The end plate being a plate-like metal member is a trailing-arm side member attached to a rear end of the cylindrical trailing arm so as to block a rear-end opening. Therefore, it is necessary that the end plate is fixedly provided in the trailing arm reliably and is reliably attached with a wheel-side member for attaching the wheels, while ensuring required mechanical strength and stiffness of the end plate. Further, because the end plate is a trailing arm-side member of a suspension system, weight saving so as not to degrade the required mechanical strength and stiffness of the end plate is desired.
Under such circumstances, Patent Literature 1 relates to a torsion beam suspension and a manufacturing method thereof, and discloses a configuration in which a wheel attaching flange 2 is welded to a pipe-like side arm 1, and a protruded surface 3 is formed on the wheel attaching flange 2 on the side facing the pipe-like side arm 1.